1. Field of the Invention
This invention is concerned with a magnetic toner which may be used for electrophotographic methods, electronic printing methods, electrostatic recording methods, magnetic recording methods and the like, and more particularly, to a magnetic color toner.
2. Description of the Prior Art
The electrophotographic method comprises producing electrostatic latent images by utilizing a photoconductive member such as cadmium sulfide, polyvinylcarbazole, selenium, zinc oxide and the like, for example, imparting uniformly electric charge onto the photoconductive layer to form electrostatic latent images by imagewise exposure, and developing the latent image with toner particles charged oppositely to the charge of the latent images, and if desired, transferring the developed images onto a receiving sheet followed by fixing.
Electronic printing methods comprise utilizing electric field to introduce charged powdered toner onto a recording member and fixing and thereby printing as disclosed in West German Pat. No. 1203808.
Electrostatic recording methods comprise imagewise imparting electric charge to a dielectric member, attaching charged toner particles thereto and fixing the toner particle. Magnetic printing also comprises forming magnetic latent images on a recording member, developing the latent images with toner powders containing a magnetic material, transferred to receiving sheet and fixing.
In case that one-component magnetic toners (not using carrier particles) are used in a developing system in the above-mentioned methods, the toner is transferred by a magnet roll to form a magnetic brush, and the magnetic brush contacts a photoconductive member such as cadmium sulfide and the like or an insulating electrostatic charge bearing member, and thereby the electric charge on the bearing member attracts the toner having an induced electrostatic charge or a triboelectric charge. As the result, the toner particles attach to the electrostatic charge bearing member to develop. This development with a one-component magnetic toner does not require a device for keeping the concentration of toner particles in the developer constant during development as used for development with a two-component developer containing carrier particles. Therefore, the developing apparatus is simple, inexpensive and small.
On the other hand, copiers have been recently used widely in various ways, and small, inexpensive multicolor copiers capable of producing colored copies are now demanded.
It is not possible to hide the color of the magnetic material by simply adding a colorant to a binder resin. For example, according to Japanese patent application Laid-open No. 42539/1976, magnetic powders are coated with a white pigment by a chemical treatment, but the color of magnetic material can not be sufficently hidden by a simple chemical treatment as far as the magnetic powder amount and the dye or pigment amount are such that they do not adversely affect the development characteristics.
In order to obtain a toner of a desired tone by the abovementioned method, the amount of the magnetic material is to be decreased or the amount of the colorant is to be increased but if the amount of the magnetic material is decreased too much, the developing property is lowered which if the amount of the colorant is increased too much, the developing property and the fixability is lowered.
When a large particle size of the magnetic material was employed and the coloring power of the magnetic material was decreased, the large particles of the magnetic material were not sufficiently dispersed in the resin and the developing properties of the magnetic toner were poor, for example, irregular images were formed, fogging was caused by the particles in which the magnetic material was not contained, and the durability was so low that the resulting images were deteriorated.
In such a manner, it has been difficult to produce a magnetic toner satisfying all of the characteristics such as developing property, tone, fixability and the like.
The present inventors have found that the above mentioned drawbacks can be solved by using magnetic powders having certain particle sizes and a sharp particle size destribution.